Recently the overheat alarm has been going off on the 1994 Mercury 3.0 Offshore 225HP carbureted 2-stroke outboard on my 1995 Boston Whaler Outrage 21 when running at high speeds. I'm reasonably certain that nothing was clogging the water intake, and the impeller was just changed during annual maintenance.
I therefore decided to inspect the thermostats. This is how one looked:
http://www.inkbox.net/whaler/parts/thermostat.jpg
I didn't test them in hot water; although this was my first time working with a thermostat they looked pretty gnarly to me, so I bought a pair of new thermostats (standard temperature in brass) along with new gaskets and installed them. We didn't have time for a sea trial right away, but I'll try that soon.
If the thermostats were in this kind of shape, I'm wondering about the poppet valve. It's harder to get to without taking the lower cowling off the outboard, so I haven't gotten a look at it yet. If the overheating incidents don't continue, one thought was that I'd just watch the water pressure gauge closely to see if it seems to indicate a properly operating poppet valve. But I'm wondering if I should take the time to drop the cowling and get a look at it too. Any advice on this?
Also, when I was buying the thermostats I asked the Merc dealer about parts for the poppet valve. My shop manual shows that, in all, the stack of parts includes a carrier, grommet, the poppet, a spring, a gasket, a relief valve plate, a diaphragm, washer, screw and gasket underneath the cover and two hold-down screws. However, the dealer told me the only parts they carry and routinely replace when it's them doing the work are the diaphragm, washer and gaskets. They'd have to special-order me, say, the poppet and spring if I wanted them. Does it sound usual just to replace that subset of the parts?
I therefore decided to inspect the thermostats. This is how one looked:
http://www.inkbox.net/whaler/parts/thermostat.jpg
I didn't test them in hot water; although this was my first time working with a thermostat they looked pretty gnarly to me, so I bought a pair of new thermostats (standard temperature in brass) along with new gaskets and installed them. We didn't have time for a sea trial right away, but I'll try that soon.
If the thermostats were in this kind of shape, I'm wondering about the poppet valve. It's harder to get to without taking the lower cowling off the outboard, so I haven't gotten a look at it yet. If the overheating incidents don't continue, one thought was that I'd just watch the water pressure gauge closely to see if it seems to indicate a properly operating poppet valve. But I'm wondering if I should take the time to drop the cowling and get a look at it too. Any advice on this?
Also, when I was buying the thermostats I asked the Merc dealer about parts for the poppet valve. My shop manual shows that, in all, the stack of parts includes a carrier, grommet, the poppet, a spring, a gasket, a relief valve plate, a diaphragm, washer, screw and gasket underneath the cover and two hold-down screws. However, the dealer told me the only parts they carry and routinely replace when it's them doing the work are the diaphragm, washer and gaskets. They'd have to special-order me, say, the poppet and spring if I wanted them. Does it sound usual just to replace that subset of the parts?